Apparatus and method for indexing sheet material

Abstract

An apparatus and associated method for indexing a strip of sheet material in fixed amounts along the support surface of a table enable an instrument supported from a carriage spanning the support surface to work on the material in precisely controlled segments and utilize one or two stops fixed in the table and movable engagement means operatively associated with the stops to limit the advancement of the sheet material as the material is indexed. The apparatus includes a transport mechanism connected for movement with the engagement means, and the sheet material is coupled to the transport mechanism for movement along the support surface. The stops define limits of travel of the engagement means and the transport mechanism to precisely fix the amount of advancement of the sheet material between work positions. The indexing operation includes positioning the engagement means at one of the limits of travel, coupling the material to the transport mechanism, and moving the mechanism and material along the support surface until the engagement means reaches another limit of travel.

I claim: 
     
       1. In an apparatus having a table defining a support on which sheet material is spread in first and second coordinate directions, an instrument for working on the sheet material spread over the table, the instrument being mounted on a first motor-controlled carriage spanning the table in the second coordinate direction and mounted on a first set of ways extending in the first coordinate direction for controllable movement back and forth parallel to the support surface and relative to the sheet material for accurate positioning and working on the sheet material, the improvement comprising: indexing means for moving the sheet material in the first of the two coordinate directions between different work positions on the table and including a second carriage also spanning the table in the second coordinate direction parallel to the first carriage and mounted to the table on a second set of ways different from but parallel to the first set for movement in the first coordinate direction, means for coupling the second carriage and the sheet material together and drive motor means connected in driving relationship with the second carriage for moving the carriage and the coupled sheet material over the table in the first coordinate direction between different work positions; and   stop means mounted to the table in noninterfering relationship with the movement of the first carriage on the first set of ways and engagement means connected for movement with the second carriage and operatively associated with the stop means for limiting the movement of the second carriage and the coupled sheet material in the first coordinate direction between work positions on the table to a fixed and predetermined amount.   
     
     
       2. Apparatus as set forth in claim 1 wherein the means for coupling the sheet material and second carriage includes means for releasably coupling the material to the carriage. 
     
     
       3. Apparatus as set forth in claim 1 wherein the engagement means is mounted for movement along an established path of the second carriage, and the stop means includes a stop mounted in the established path of movement of the engagement means for engaging the engagement means when the second carriage and the coupled sheet material have advanced the predetermined amount. 
     
     
       4. Apparatus as set forth in claim 1 wherein the the second carriage is self-propelled, and an elongated drive rack extends along the table in the first coordinate direction and is engaged by the second carriage for movement between said ends of the table, and the stop means includes first and second stops fixedly attached at opposite ends of the rack to limit the movement of the second carriage and coupled sheet material. 
     
     
       5. Apparatus as set forth in claim 1 wherein the means for coupling includes a plurality of coupling units mounted in transversely spaced series along the second carriage to travel therewith, each coupling unit including a friction shoe having a high-friction surface and means for moving the friction shoe generally toward and away from sheet material on the table and the table includes a smooth bed of material defining a support surface providing a low coefficient of friction between the sheet material and the table. 
     
     
       6. Apparatus as set forth in claim 1 further including an endless belt having a portion extending along the table in the first coordinate direction, and wherein the means for coupling comprises a clamp supported by the second carriage over the spread material and having a clamping portion movable toward and away from the belt between a coupling position at which the clamping portion holds the material against the belt and a release position at which the clamping portion is out of engagement with the material. 
     
     
       7. The apparatus of claim 6 wherein the endless belt is magnetically permeable and the clamping portion is an electrically actuated magnet for magnetically coupling the material to the second carriage. 
     
     
       8. In an apparatus having a table defining a support surface on which sheet material is spread in two coordinate directions, an instrument for working on the sheet material spread on the table, and the instrument being mounted for controllable movement back and forth parallel to the support surface and relative to the sheet material for accurate positioning and working on the sheet material, the improvement comprising: indexing means for moving the sheet material in one of the two coordinate directions between different work positions on the table and including a movable transport mechanism having an endless belt with one portion to which the sheet material is coupled extending over the support surface, means for coupling the endless belt and the sheet material together, a drum rotatably supported in the table and engaged with the belt, and drive motor means connected in driving relationship through the drum with the belt for moving the belt and the coupled sheet material over the table in the one coordinate direction between different work positions; and   stop means mounted to the table and engagement means connected for movement with the transport mechanism and operatively associated with the stop means for limiting the movement of the sheet material in the one coordinate direction between work positions on the table to a fixed and predetermined amount.   
     
     
       9. Apparatus as set forth in claim 8 wherein the engagement means is fixedly attached the drum to follow a circular path as the drum is rotated by the drive motor means and as the belt portion is moved along the support surface; and the stop means includes a solenoid-activated plunger movable between a position at which the plunger is in the circular path of movement of the engagement means and a position at which the plunger is out of the path of the engagement means.   
     
     
       10. A method of indexing a strip of sheet material a fixed amount in the lengthwise direction of the strip between different work positions along the support surface of a table, the table being part of an apparatus for performing a work operation on the sheet material in segments by means of a first transport mechanism moving a work tool over the table parallel to the lengthwise direction of the strip, the method comprising the steps of: providing the apparatus with a second transport mechanism and mounting the second mechanism for movement relative to the table in the lengthwise direction;   further providing the apparatus with stop means and cooperative engagement means associated with the second transport mechanism and connecting the engagement means for movement with the movable second mechanism between limits of travel established by engagement of the engagement means with the stop means thereby limiting the movement of the movable second transport mechanism to a fixed and predetermined amount without limiting the movement of the first transport mechanism;   positioning the second transport mechanism and the engagement means in engagement with the stop means at one limit of travel;   coupling the sheet material and the second transport mechanism together;   moving the second transport mechanism to advance the sheet material along the support surface of the table and the engagement means from the one limit toward the other; and   halting the movement of the second transport mechanism and the material coupled therewith when the engagement means reaches the other limit of travel whereby the material is advanced a fixed and predetermined amount.   
     
     
       11. The method of indexing as defined in claim 10 including the step of releasing the sheet material from the second transport mechanism after the step of halting. 
     
     
       12. The method of indexing as defined in claim 11 further including the steps of returning the second transport mechanism and the engagement means from the one limit to the other and thereafter repeating in sequence the steps of coupling, moving, and halting to index the material by another fixed and predetermined amount. 
     
     
       13. A method for precisely indexing as defined in claim 10 wherein the step of coupling occurs simultaneously with the step of positioning. 
     
     
       14. The method of indexing as defined in claim 10 wherein the limits of travel are established by an engagement means which travels with the movement of the second transport mechanism in a closed path, and the stop means is movable into and out of the path of the engagement means.